1. Field of the Invention
The present invention relates to an information processing system including an arithmetic processing unit, a master control unit for executing processing in accordance with an instruction from the arithmetic processing unit, and a slave control unit for controlling a load in accordance with an instruction from the arithmetic processing unit.
2. Description of the Related Art
An image forming apparatus using electrophotography includes a plurality of functions necessary for image formation, such as a conveying function to convey a recording material such as a sheet, an image forming function to generate an image, and a fixing function to fix an image on a recording material. When those functions are achieved by a single central processing unit (CPU), the processing load of the CPU increases, thus making the overall processing slow. In addition, arrangement of wiring from the CPU to a board where an actuator such as a motor is connected becomes complicated. Therefore, it is desired to execute distributed control on the operation of the image forming apparatus by using a plurality of control modules that achieve those functions. Each control module includes a CPU that executes processing for achieving the associated function.
Serial communications are sometimes used for transmission and reception of data between the CPUs of the plurality of control modules. As the number of loads such as motors controlled by the respective CPUs increases, a frequency of a control instruction using serial communications increases. Therefore, in addition to memory used for a transmission instruction through the serial communications, memory for addresses and data for respective control modules used for the control instruction increases, which leads to a cost increase. Further, the CPU needs to wait for the next transmission until the serial communications are completed, which leads to reduction in productivity. Japanese Patent Application Laid-Open No. 63-224545 proposes a technology for effectively using memory by requesting a transmitting end to pause the transmission when the memory for transmission through the serial communications has no room.
In a data communication technology using the serial communications disclosed in Japanese Patent Application Laid-Open No. 63-224545, the communications are stopped more frequently as an amount of data being transmitted increases. Therefore, when the technology disclosed in Japanese Patent Application Laid-Open No. 63-224545 is applied to an image forming apparatus, there is a problem in that, for example, jamming or the like occurs due to a delay in control of a motor for conveying a recording material. Increasing a capacity of memory as a countermeasure against the above-mentioned problem leads to the cost increase, which is not preferred for merchandise.